Zoology MCQs for NEET — Practice Questions with Answers

Tyrosine is the precursor for several important substances, including adrenaline (a hormone and neurotransmitter), thyroxin (a thyroid hormone), and melanin (a pigment responsible for skin, hair, and eye color). This amino acid undergoes various biochemical modifications to form these compounds.

Tetany is a condition caused by low levels of calcium in the blood, which can result from a deficiency of the parathyroid hormone. The parathyroid hormone plays a crucial role in regulating calcium levels in the blood.

Luteinizing hormone (LH) is essential for ovulation. A deficiency in LH can lead to the failure of ovulation, which is a critical process in the female reproductive system.

Hormones can be chemically classified into proteins, steroids, and biogenic amines. For example, insulin is a protein hormone, cortisol is a steroid hormone, and adrenaline is a biogenic amine.

The hormone responsible for initiating rapid action in response to stress or fear, such as climbing down the stairs quickly during an earthquake, is adrenaline. Adrenaline, also known as epinephrine, is produced by the adrenal glands and plays a key role in the 'fight or flight' response by increasing heart rate, blood flow to muscles, and releasing glucose for immediate energy.

Matching the items from list-I with list-II correctly:
a) Adrenaline - Accelerates heart beat (2)
b) Hyperparathyroidism - Demineralisation (5)
c) Oxytocin - Child birth (4)
d) Hypothyroidism - Myxoedema (1)
e) Aldosterone - Salt-water balance (3)
Therefore, the correct matching option is (a - 2), (b - 5), (c - 4), (d - 1), (e - 3).

The parathyroid gland primarily functions to regulate calcium levels in the blood. It produces parathyroid hormone (PTH), which increases blood calcium levels by stimulating osteoclasts to break down bone and release calcium, enhancing calcium reabsorption in the kidneys, and increasing calcium absorption in the intestines. Thus, the correct answer is that the parathyroid gland increases blood Ca⁺² level.

Collar cells, also known as choanocytes, are specialized cells found in sponges (Phylum Porifera). These cells have a flagellum surrounded by a collar of microvilli and are responsible for creating water currents and capturing food particles.

The canal system is a characteristic feature of sponges (Phylum Porifera). This system consists of a network of channels and chambers through which water circulates, allowing sponges to filter feed and exchange gases.